Catalytic fuel tank inerting system

ABSTRACT

A fuel tank inerting system is disclosed. The system includes a fuel tank and a catalytic reactor. The catalytic reactor is arranged to receive a first reactant from a first reactant source and to receive a second reactant from a second reactant source, and to react the first and second reactants to generate an inert gas. The system also includes an inert gas flow path from the catalytic reactor to the fuel tank. The catalytic reactor includes first, second, and third flow paths. The first flow path includes receives a first reactant and includes a reactive flow path including a catalyst. The second flow path receives a second reactant source and is in operative fluid communication with the first flow path through a first barrier between the first and second flow paths that is permeable to the second reactant. The third flow path receives a fluid coolant.

BACKGROUND

The subject matter disclosed herein generally relates to fuel handlingsystems, and more particularly to fuel tank inerting systems such asused on aircraft.

It is recognized that fuel vapors within fuel tanks become combustiblein the presence of oxygen. An inerting system decreases the probabilityof combustion of flammable materials stored in a fuel tank bymaintaining a chemically non-reactive or inert gas, such asnitrogen-enriched air, in the fuel tank vapor space, also known asullage. Three elements are required to initiate and sustain combustion:an ignition source (e.g., heat), fuel, and oxygen. Combustion may beprevented by reducing any one of these three elements. If the presenceof an ignition source cannot be prevented within a fuel tank, then thetank may be made inert by: 1) reducing the oxygen concentration, 2)reducing the fuel concentration of the ullage to below the lowerexplosive limit (LEL), or 3) increasing the fuel concentration to abovethe upper explosive limit (UEL). Many systems reduce the risk ofcombustion by reducing the oxygen concentration by introducing an inertgas such as nitrogen-enriched air (NEA) to the ullage, therebydisplacing oxygen with a mixture of nitrogen and oxygen at targetthresholds for avoiding explosion or combustion.

It is known in the art to equip aircraft with onboard inert gasgenerating systems, which supply nitrogen-enriched air to the vaporspace (i.e., ullage) within the fuel tank. The nitrogen-enriched air hasa substantially reduced oxygen content that reduces or eliminatescombustible conditions within the fuel tank. Onboard inert gasgenerating systems typically use membrane-based gas separators. Suchseparators contain a membrane that is permeable to oxygen and watermolecules, but relatively impermeable to nitrogen molecules. A pressuredifferential across the membrane causes oxygen molecules from air on oneside of the membrane to pass through the membrane, which formsoxygen-enriched air (OEA) on the low-pressure side of the membrane andNEA on the high-pressure side of the membrane. The requirement for apressure differential necessitates a source of compressed or pressurizedair. Bleed air from an aircraft engine or from an onboard auxiliarypower unit can provide a source of compressed air; however, this canreduce available engine power and also must compete with other onboarddemands for compressed air, such as the onboard air environmentalconditioning system and anti-ice systems. Moreover, certain flightconditions such as during aircraft descent can lead to an increaseddemand for NEA at precisely the time when engines could be throttledback for fuel savings so that maintaining sufficient compressed airpressure for meeting the pneumatic demands may come at a significantfuel burn cost. Additionally, there is a trend to reduce or eliminatebleed-air systems in aircraft; for example Boeing's 787 has a no-Needsystems architecture, which utilizes electrical systems to replace mostof the pneumatic systems to improve fuel efficiency, as well as reduceweight and lifecycle costs. Other aircraft architectures may adoptlow-pressure bleed configurations where engine design parameters allowfor a bleed flow of compressed air, but at pressures less than the 45psi air (unless stated otherwise, “psi” as used herein means absolutepressure in pounds per square inch, i.e., psia) that has been typicallyprovided in the past to conventional onboard environmental controlsystems. A separate compressor or compressors can be used to providepressurized air to the membrane gas separator, but this undesirablyincreases aircraft payload, and also represents another onboard devicewith moving parts that is subject to maintenance issues or devicefailure.

BRIEF DESCRIPTION

A fuel tank inerting system is disclosed. The system includes a fueltank and a catalytic reactor. The catalytic reactor is arranged toreceive a first reactant from a first reactant source and to receive asecond reactant from a second reactant source, and to react the firstand second reactants to generate an inert gas. The system also includesan inert gas flow path from the catalytic reactor to the fuel tank. Thecatalytic reactor includes first, second, and third flow paths. Thefirst flow path comprises a first inlet in operative fluid communicationthe first reactant source, a first outlet in operative fluidcommunication with the inert gas flow path, and a reactive flow pathincluding a catalyst between the first inlet and the first outlet. Thesecond flow path comprises a second inlet in operative fluidcommunication with the second reactant source and is in operative fluidcommunication with the first flow path through a first barrier betweenthe first and second flow paths that is permeable to the secondreactant. The third flow path comprises a third inlet in operative fluidcommunication with a fluid coolant, and a third outlet, said third flowpath in operative thermal communication with the first flow path.

In some embodiments, the first reactant comprises air, and the secondreactant comprises fuel.

In some embodiments, the system comprises liquid fuel on the second flowpath.

In some embodiments, the system comprises vaporized fuel on the secondflow path.

In any one or combination of the foregoing embodiments, the firstreactant comprises vaporized fuel, and the second reactant comprisesoxygen.

In any one or combination of the foregoing embodiments, the second flowpath is devoid of outlets except through the first barrier.

In any one or combination of the foregoing embodiments, the catalyticreactor comprises a plurality of said first flow paths, or a pluralityof said second flow paths, or a plurality of said third flow paths, orany combination thereof

In any one or combination of the foregoing embodiments, the systemfurther comprises a heat source or a heat sink in operative thermalcommunication with either or both of the first reactant or the secondreactant delivered to the catalytic reactor inlet.

In any one or combination of the foregoing embodiments, the first,second, and third flow paths are arranged in the catalytic reactor in aplanar configuration.

In any one or combination of the foregoing embodiments, at least one ofthe first flow path, the second flow path, or the third flow pathcomprises an internal space of a tubular conduit disposed in thecatalytic reactor.

In some embodiments comprising a tubular conduit, another of the firstflow path, the second flow path, or the third flow path comprises aspace in the catalytic the catalytic reactor external to the tubularconduit.

In any one or combination of the foregoing embodiments comprising atubular conduit, the third flow path comprises the internal space of thetubular conduit.

In any one or combination of the foregoing embodiments comprising atubular conduit, the first flow path comprises the catalyst disposed ina fluid-permeable arrangement on an exterior surface of the tubularconduit.

In any one or combination of the foregoing embodiments comprising atubular conduit, the third flow path comprises the internal space of thetubular conduit, the first flow path comprises the catalyst disposed ina fluid-permeable arrangement on an exterior surface of the tubularconduit, and the second flow path comprises a space in the catalyticexternal to the tubular conduit.

In any one or combination of the foregoing embodiments, the systemfurther comprises a second barrier between the second flow path and thethird flow path, said second barrier being thermally conductive andimpermeable to fluids.

In any one or combination of the foregoing embodiments, the systemfurther comprises a controller configured to control at least one of aflow rate of the first reactant, a flow rate of the second reactant, ora flow rate of the fluid coolant.

In some embodiments, the controller is configured to control at leastone of the first reactant flow rate, the second reactant flow rate, orthe fluid coolant flow rate to maintain a temperature in the catalyticreactor or at an outlet of the catalytic reactor.

In some embodiments the controller is configured to maintain thetemperature at less than 300° C.

Also disclosed is a method of operating the fuel tank inerting system ofany one or combination of the foregoing embodiments, comprisingdelivering the first and second reactants to the first and second inletsand delivering the fluid coolant to the third inlet, reacting the firstand second reactants along the reactive flow path to produce inert gas,and delivering the inert gas through the inert gas flow path to the fueltank.

In some embodiments, the method further comprising controlling at leastone of a flow rate of the first reactant, a flow rate of the secondreactant, or a flow rate of the fluid coolant to maintain a temperaturein the catalytic reactor or at an outlet of the catalytic reactor

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way.With reference to the accompanying drawings, like elements are numberedalike:

FIG. 1A is a schematic illustration of an aircraft that can incorporatevarious embodiments of the present disclosure;

FIG. 1B is a schematic illustration of a bay section of the aircraft ofFIG. 1A;

FIG. 2 is a schematic illustration of an example embodiment of a fueltank inerting system;

FIG. 3 is a schematic illustration of an example embodiment of acatalytic reactor of a fuel tank inerting system; and

FIG. 4 is a schematic illustration of another example embodiment of acatalytic reactor of a fuel tank inerting system,

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosedapparatus and method are presented herein by way of exemplification andnot limitation with reference to the Figures.

As shown in FIGS. 1A-1B, an aircraft 101 can include one or more bays103 beneath a center wing box. The bay 103 can contain and/or supportone or more components of the aircraft 101. For example, in someconfigurations, the aircraft 101 can include environmental controlsystems and/or fuel inerting systems within the bay 103. As shown inFIG. 1B, the bay 103 includes bay doors 105 that enable installation andaccess to one or more components (e.g., environmental control systems,fuel inerting systems, etc.). During operation of environmental controlsystems and/or fuel inerting systems of the aircraft 101, air that isexternal to the aircraft 101 can flow into one or more ram air inlets107. The outside air may then be directed to various system components(e.g., environmental conditioning system (ECS) heat exchangers) withinthe aircraft 101. Some air may be exhausted through one or more ram airexhaust outlets 109.

Also shown in FIG. 1A, the aircraft 101 includes one or more engines111. The engines 111 are typically mounted on wings of the aircraft 101,but may be located at other locations depending on the specific aircraftconfiguration. In some aircraft configurations, air can be bled from theengines 111 and supplied to environmental control systems and/or fuelinerting systems, as will be appreciated by those of skill in the art.

As noted above, typical air separation modules operate using pressuredifferentials to achieve desired air separation. Such systems require ahigh pressure pneumatic source to drive the separation process acrossthe membrane. Further, the hollow fiber membrane separators commonlyused are relatively large in size and weight, which is a significantconsideration with respect to aircraft (e.g., reductions in volume andweight of components can improve flight efficiencies). Embodimentsprovided herein can provide reduced volume and/or weight characteristicsof air separation modules for aircraft. In accordance with someembodiments of the present disclosure, the typical hollow fiber membraneseparator can be replaced by a catalytic system (e.g., CO₂ generationsystem), which can be, for example, smaller, lighter, more durable,and/or more efficient than the typical fiber membrane separators. Thecatalytic system can be used on any fuel tank system, whether stationary(e.g., a tank farm) or on a vehicle with on-board fuel (i.e., fueledvehicle) such as an aircraft, ship, submarine or other marine vehicle,or land vehicle.

A function of fuel tank flammability reduction systems in accordancewith embodiments of the present disclosure is accomplished by reacting asmall amount of a first reactant (e.g., fuel vapor) with a secondreactant (e.g., oxygen from an oxygen source such as an air source). Forthe sake of convenience, the discussion below refers to fuel as thefirst reactant and oxygen or air as the second reactant; however, theterms “first” and “second” are of course arbitrary, and the firstreactant can be oxygen or air and the second reactant can be fuel. Inany case, the product of the reaction is carbon dioxide and water vapor.The source of the second reactant (e.g., air) can be bleed air or anyother source of air containing oxygen, including, but not limited to,high-pressure sources (e.g., engine), bleed air, cabin air, etc. Acatalyst material such as a noble metal catalyst is used to catalyze thechemical reaction. The carbon dioxide that results from the reaction isan inert gas that is mixed with nitrogen naturally found infresh/ambient air, and is directed back within a fuel tank to create aninert environment within the fuel tank, thus reducing a flammability ofthe vapors in the fuel tank.

As mentioned above, a catalyst is used to catalyze a chemical reactionbetween oxygen (O₂) and fuel to produce carbon dioxide (CO₂) and water.The source of O₂ used in the reaction can come from any of a number ofair sources, including, but not limited to, pneumatic sources on anaircraft that supply air at a pressure greater than ambient. Fuel forthe reaction can be provided from the vapor space of the fuel tank or byvaporizing liquid fuel from the aircraft fuel tank. The fuel can beheated to promote vaporization of the fuel, such as by using an electricheater, as shown and described in some embodiments of the presentdisclosure. Any inert gas species that are present with the reactants(for example, nitrogen) will not react and will thus pass through thecatalyst unchanged.

In some embodiments, the catalyst can be in a form factor that acts as aheat exchanger. For example, in one non-limiting configuration, a platefin heat exchanger configuration is employed wherein a hot side of theheat exchanger would be coated with catalyst material. In sucharrangement, the cold side of the catalyst heat exchanger can be fedwith a cool air source, such as ram air or some other source of coldair. The air through the cold side of the heat exchanger can becontrolled such that the temperature of a hot, mixed-gas stream is hotenough to sustain a desired chemical reaction within or at the catalyst.Further, the cooling air can be used to maintain a cool enoughtemperature to enable removal of heat generated by exothermic reactionsat the catalyst.

The catalytic chemical reaction between fuel and air also generateswater. Water in the fuel tank can be undesirable. Thus, in accordancewith embodiments of the present disclosure, the water from a product gasstream (e.g., exiting the catalyst) can be removed through variousmechanisms, including, but not limited to, condensation. The product gasstream can be directed to enter a heat exchanger downstream from thecatalyst that is used to cool the product gas stream such that the watervapor condenses out of the product gas stream. The liquid water can thenbe drained overboard. In some embodiments, an optional water separatorcan be used to augment or provide water separation from the productstream.

Aircraft fuel tanks are typically vented to ambient pressure. Ataltitude, pressure inside the fuel tank is very low and is roughly equalto ambient pressure. However, during descent, the pressure inside thefuel tank needs to rise to equal ambient pressure at sea level (or atwhatever altitude the aircraft is landing). This change in pressurerequires gas entering the tank from outside to equalize with thepressure in the tank. When air from outside enters the tank, water vaporis normally present with it. Water can become trapped in the fuel tankand cause problems. In accordance with embodiments of the presentdisclosure, to prevent water from entering the fuel tanks, the fuelinerting systems of the present disclosure can repressurize the fueltanks with dry inert gas that is generated as described above and below.The repressurization can be accomplished by using a flow control valveto control the flow of inert gas into the fuel tank such that a positivepressure is constantly maintained in the fuel tank. The positivepressure within the fuel tank can prevent air from entering the fueltank from outside during descent and therefore prevent water in the airoutside the fuel tank from entering the fuel tank.

FIG. 2 is a schematic illustration of a flammability reduction orinerting system 200 utilizing a catalytic reaction between first andsecond reactants to produce inert gas in accordance with an embodimentof the present disclosure. The inerting system 200, as shown, includes afuel tank 202 having fuel 204 therein. As the fuel 204 is consumedduring operation of one or more engines, an ullage space 206 formswithin the fuel tank 202. To reduce flammability risks associated withvaporized fuel that may form within the ullage space 206, an inert gascan be generated and fed into the ullage space 206.

The inerting system 200 utilizes the catalytic reactor 222 to catalyze achemical reaction between oxygen (second reactant 218) and fuel (firstreactant 216) to produce carbon dioxide for the inert gas (inert gas234) and water (byproduct 236). The source of the second reactant 218(e.g., oxygen) used in the reaction can come from any source on theaircraft that is at a pressure greater than ambient, including but notlimited to bleed air from an engine, cabin air, high pressure airextracted or bled from an engine, etc. (i.e., any second reactant source220 can take any number of configurations and/or arrangements). Evennon-air oxygen sources can be used, and “air” is used herein as ashort-hand term for any oxygen-containing gas. As described in greaterdetail below, in some embodiments fuel can be introduced to a catalyticreactor in vapor or liquid form. To provide fuel in vapor form, aninerting fuel 208 can be extracted from the fuel tank 202 and into anevaporator container 210. The inerting fuel 208 within the evaporatorcontainer 210 can be heated using the electric heater 214.

With continued reference to FIG. 2, the first and second reactants areintroduced to the catalytic reactor 222, catalyzing a chemical reactionthat transforms the reactants into the inert gas 234 and the byproduct236 (e.g., water vapor). It is noted that any inert gas species that arepresent in the reactants (for example, nitrogen from the air) will notreact and will thus pass through the catalytic reactor 222 unchanged. Insome embodiments, the catalytic reactor 222 is in a form factor thatacts as a heat exchanger. For example, one non-limiting configurationmay be a plate fin heat exchanger wherein the hot side of the heatexchanger would be coated with the catalyst material. Those of skill inthe art will appreciate that various types and/or configurations of heatexchangers may be employed without departing from the scope of thepresent disclosure. The cold side of the catalyst heat exchanger can befed with the cooling air 226 from the cool air source 228 (e.g., ram airor some other source of cold air). The air through the cold side of thecatalyst heat exchanger can be controlled such that the reactortemperature is hot enough to sustain the chemical reaction desiredwithin the catalytic reactor 222, but cool enough to remove the heatgenerated by the exothermic reaction, thus maintaining aircraft safetyand materials from exceeding maximum temperature limits.

The catalytic reactor 222 can be temperature controlled to ensure adesired chemical reaction efficiency such that an inert gas can beefficiently produced by the inerting system 200 from the reactants.Accordingly, cooling air 226 can be provided to extract heat from thecatalytic reactor 222 to achieve a desired thermal condition for thechemical reaction within the catalytic reactor 222. The cooling air 226can be sourced from a cool air source 228. A catalyzed mixture 230leaves the catalytic reactor 222 and is passed through a heat exchanger232. The heat exchanger 232 operates as a condenser on the catalyzedmixture 230 to separate out an inert gas 234 and a byproduct 236 (e.g.,water). A cooling air is supplied into the heat exchanger 232 to achievethe condensing functionality. In some embodiments, as shown, a coolingair 226 can be sourced from the same cool air source 228 as thatprovided to the catalytic reactor 222, although in other embodiments thecool air sources for the two components may be different. The byproduct236 may be water vapor, and thus in the present configuration shown inFIG. 2, an optional water separator 238 is provided downstream of theheat exchanger 232 to extract the water from the catalyzed mixture 230,thus leaving only the inert gas 234 to be provided to the ullage space206 of the fuel tank 202.

A flow control valve 248 located downstream of the heat exchanger 232and optional water separator 238 can meter the flow of the inert gas 234to a desired flow rate. An optional boost fan 240 can be used to boostthe gas stream pressure of the inert gas 234 to overcome a pressure dropassociated with ducting between the outlet of the heat exchanger 232 andthe discharge of the inert gas 234 into the fuel tank 202. The flamearrestor 242 at an inlet to the fuel tank 202 is arranged to prevent anypotential flames from propagating into the fuel tank 202.

Typically, independent of any aircraft flammability reduction system(s),aircraft fuel tanks (e.g., fuel tank 202) need to be vented to ambientpressure. Thus, as shown in FIG. 2, the fuel tank 202 includes a vent250. At altitude, pressure inside the fuel tank 202 is very low and isroughly equal to ambient pressure. During descent, however, the pressureinside the fuel tank 202 needs to rise to equal ambient pressure at sealevel (or whatever altitude the aircraft is landing at). This requiresgas entering the fuel tank 202 from outside to equalize with thepressure in the tank. When air from outside enters the fuel tank 202,water vapor can be carried by the ambient air into the fuel tank 202. Toprevent water/water vapor from entering the fuel tank 202, the inertingsystem 200 can repressurize the fuel tank 202 with the inert gas 234generated by the inerting system 200. This is accomplished by using thevalves 248. For example, one of the valves 248 may be a flow controlvalve 252 that is arranged fluidly downstream from the catalytic reactor222. The flow control valve 252 can be used to control the flow of inertgas 234 into the fuel tank 202 such that a slightly positive pressure isalways maintained in the fuel tank 202. Such positive pressure canprevent ambient air from entering the fuel tank 202 from outside duringdescent and therefore prevent water from entering the fuel tank 202.

A controller 244 can be operably connected to the various components ofthe inerting system 200, including, but not limited to, the valves 248and the sensors 246. The controller 244 can be configured to receiveinput from the sensors 246 to control the valves 248 and thus maintainappropriate levels of inert gas 234 within the ullage space 206.Further, the controller 244 can be arranged to ensure an appropriateamount of pressure within the fuel tank 202 such that, during a descentof an aircraft, ambient air does not enter the ullage space 206 of thefuel tank 202.

In some embodiments, the inerting system 200 can supply inert gas tomultiple fuel tanks on an aircraft. As shown in the embodiment of FIG.2, an inerting supply line 254 fluidly connects the fuel tank 202 to theevaporator container 210. After the inert gas 234 is generated, theinert gas 234 will flow through a fuel tank supply line 256 to supplythe inert gas 234 to the fuel tank 202 and, optionally, additional fueltanks 258.

With reference now to FIG. 3, a portion of a catalytic reactor 322 isshown with greater details. The components and flow paths in FIG. 3 arearranged in a planar configuration shown in a cross-sectional view suchas a top or side view. As shown in FIG. 3, first flow paths 302 and 304introduce a first reactant to a catalyst 306 at inlets 303 and 305, anddischarge inert gas at outlets 307 and 309, respectively. The catalyst306 is disposed in an arrangement so as to be permeable to the flow ofthe first reactant. For example, the catalyst can be disposed as apowder, pellets, a foam, a coated honeycomb, or a coating on a wallsurface adjacent to an open flow path space. Examples of catalystsinclude noble metals (e.g. Pt, Pd, Ru, Au, Ag, Rh and combinationsthereof), either self-supporting or on a support such as alumina.Transition metal oxides such as manganese oxide can also be used as acatalyst. Catalyst composition variations can be provided with numerousvariations on catalyst metal and dopants. In some embodiments, anupstream catalyst bed or reactor section can include a lower activitytransition metal oxide catalyst such as manganese oxide and a downstreambed or section can include a higher activity noble metal catalyst suchas a platinum or palladium catalyst.

As further shown in FIG. 3, a second reactant is delivered to a secondflow path 308. The second flow path 308 is separated from the first flowpaths 302/304 by a barrier 310 that is permeable to the second reactant,and the second reactant is shown transporting across the barrier alongflow paths 312. The second flow path can include an outlet similar tothe first flow path outlets 307/309, or can be dead-ended so that all ofthe reactant on the flow path is directed along flow paths 312. In someembodiments, the second flow path can be dead-ended (i.e., devoid ofoutlets except for across the barrier 310) or can include an outlet withcontrollable flow (e.g., a control valve downstream of the outlet) as acontrol feature to control the amount of reactant that enters thereactive first flow paths 302/304 along flow paths 312.

In some embodiments, the barrier can be in the form of a gas transportmembrane. Gas transport membranes can rely on one or more physicalphenomena for selectivity in transportation of gases across themembrane. In some embodiments, gas transport membranes can rely onporosity with molecular size-selective pathways to provide transport ofmolecules across the membrane. Examples of such membranes include aporous polymer matrix (e.g., formed from PEEK, or a polyimide or otherhigh temperature polymer such as polybenzimidazole tolerant of thereaction temperatures) or a porous metal or porous ceramic (e.g.,zeolite) or other oxide or a carbon based porous membrane or a compositemembrane (for example nanocomposite polymer/carbon or polymer/silica)tailored to provide adequate transport performance and durability.

So-called reverse selective membranes rely on phenomena including thesolubility of the gas molecules in the membrane material to providetransport through the membrane for molecules having solubility in themembrane. Examples of such membranes include organic polymer membranesthat provide solubility for organic fuel vapor molecules to promotetransport across the membrane. Solubility and pore size factors can beused to promote selectivity for types of molecules, for example toinhibit transport of first reactant across the membrane to the secondflow path, or to prevent transport of contaminants (e.g., sulfurcontaminants in fuel) across the membrane. Composite materialscomprising organic and inorganic materials can also be used. Themembrane can include any of the above materials, alone or in combinationwith each other or other selective materials. Combinations of differentmaterials can be integrated into a single membrane structure (e.g., inlayers, or zones in the x-y plane of a membrane structure), or can bedisposed in series or in parallel as separate membrane structures ormodules.

With continued reference to FIG. 3, a third flow path 314 is shown witha flowing fluid coolant. Any fluid coolant can be used, such as air(e.g., ram air) or a heat transfer fluid in a loop communication with aheat sink (not shown). The third flow path is shown in FIG. 3 with afluid-impermeable barrier 316 between the third flow path and the firstflow path. The barrier 316 can be made from any thermally conductivematerial such as a thermally conductive metal. In some embodiments, thethird flow path can be controllably dead-ended or flow-limited (e.g., inresponse to cooling demand) to control the amount of coolant that flowsalong the third flow path 314. At this point, it should be noted thatthe configuration pattern of components shown in FIG. 3 can be extendedwith additional components and flow paths. For example, FIG. 3 showsadditional unnumbered catalyst and first flow path to the right-handside of FIG. 3 and an additional unnumbered third flow path to theleft-hand side of FIG. 3. In embodiments with such multiple flow paths,any one or a plurality of the second or third flow paths can bedea-ended or have an open or controllable outlet as described above.

In some embodiments, a reactor can be configured with a plurality oftubular conduits as shown in the cross-sectional end view of reactor 422in FIG. 4. As shown in FIG. 4, a plurality of conduits 416 (forconvenience, only one of the conduits in FIG. 4 is labeled anddiscussed) are disposed inside a reactor housing 403, with a third flowpath 414 with flowing fluid coolant on the inside of the conduit. Acatalyst 406 is disposed on the exterior of the conduit, providing afirst reactant flow path 402, which is separated from a second reactantflow path 408 in the space in the reactor housing 403 external to theconduits by a barrier 410 that is permeable to the second reactant. Aswith FIG. 3, the second flow path 408 can be open or dead-ended at anaxial terminus or can have a flow controlled axially-terminal outlet,and any one or combination of the third flow paths 414 can becontrollably dead-ended or flow-limited in response to cooling demand.

In some embodiments, a technical effect can be provided of managing orcontrolling reactor temperature. This can be accomplished, for example,by controlling the respective flows of one or more of the first andsecond reactants and the fluid coolant. In some embodiments, controller244 (FIG. 2) can be configured to control one or more of these flowrates to maintain a temperature in the catalytic reactor (e.g., alongthe first flow path) or at an outlet of the reactor (e.g., outlet of thefirst flow path). For example, temperature can be reduced by increasingthe flow of coolant, or decreasing the flow of fuel and/or air-O₂. Insome embodiments, the flow rates can be controlled to maintain atemperature at less than or equal to 325° C. In some embodiments, theflow rates can be controlled to maintain a temperature at less than orequal to 300° C. In some embodiments, the flow rates can be controlledto maintain a temperature at less than or equal to 275° C. In someembodiments, the flow rates can be controlled to maintain a temperatureat less than or equal to 250° C.

The term “about”, if used, is intended to include the degree of errorassociated with measurement of the particular quantity based upon theequipment available at the time of filing the application. For example,“about” can include a range of ±8% or 5%, or 2% of a given value.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,element components, and/or groups thereof

While the present disclosure has been described with reference to anexemplary embodiment or embodiments, it will be understood by thoseskilled in the art that various changes may be made and equivalents maybe substituted for elements thereof without departing from the scope ofthe present disclosure. In addition, many modifications may be made toadapt a particular situation or material to the teachings of the presentdisclosure without departing from the essential scope thereof.Therefore, it is intended that the present disclosure not be limited tothe particular embodiment disclosed as the best mode contemplated forcarrying out this present disclosure, but that the present disclosurewill include all embodiments falling within the scope of the claims.

What is claimed is:
 1. A fuel tank inerting system, comprising a fueltank; a catalytic reactor arranged to receive a first reactant from afirst reactant source and to receive a second reactant from a secondreactant source, and to react the first and second reactants to generatean inert gas; and an inert gas flow path from the catalytic reactor tothe fuel tank, wherein the catalytic reactor comprises: a first flowpath comprising a first inlet in operative fluid communication the firstreactant source, a first outlet in operative fluid communication withthe inert gas flow path, and a reactive flow path including a catalystbetween the first inlet and the first outlet; a second flow pathcomprising a second inlet in operative fluid communication with thesecond reactant source, said second flow path in operative fluidcommunication with the first flow path through a first barrier betweenthe first and second flow paths that is permeable to the secondreactant; and a third flow path comprising a third inlet in operativefluid communication with a fluid coolant, and a third outlet, said thirdflow path in operative thermal communication with the first flow path.2. The fuel tank inerting system of claim 1, wherein the first reactantcomprises air, and the second reactant comprises fuel.
 3. The fuel tankinerting system of claim 2, comprising liquid fuel on the second flowpath.
 4. The fuel tank inerting system of claim 2, comprising vaporizedfuel on the second flow path.
 5. The fuel tank inerting system of claim1, wherein the first reactant comprises vaporized fuel, and the secondreactant comprises oxygen.
 6. The fuel tank inerting system of claim 1,wherein the second flow path is devoid of outlets except through thefirst barrier.
 7. The fuel tank inerting system of claim 1, wherein thecatalytic reactor comprises a plurality of said first flow paths, or aplurality of said second flow paths, or a plurality of said third flowpaths, or any combination thereof.
 8. The fuel tank inerting system ofclaim 1, further comprising a heat source or a heat sink in operativethermal communication with either or both of the first reactant or thesecond reactant delivered to the catalytic reactor inlet.
 9. The fueltank inerting system of claim 1, wherein said first, second, and thirdflow paths are arranged in the catalytic reactor in a planarconfiguration.
 10. The fuel tank inerting system of claim 1, wherein atleast one of the first flow path, the second flow path, or the thirdflow path comprises an internal space of a tubular conduit disposed inthe catalytic reactor.
 11. The fuel tank inerting system of claim 11,wherein another of the first flow path, the second flow path, or thethird flow path comprises a space in the catalytic the catalytic reactorexternal to the tubular conduit.
 12. The fuel tank inerting system ofclaim 11, wherein the third flow path comprises the internal space ofthe tubular conduit.
 13. The fuel tank inerting system of claim 11,wherein the first flow path comprises the catalyst disposed in afluid-permeable arrangement on an exterior surface of the tubularconduit.
 14. The fuel tank inerting system of claim 11, wherein thethird flow path comprises the internal space of the tubular conduit, thefirst flow path comprises the catalyst disposed in a fluid-permeablearrangement on an exterior surface of the tubular conduit, and thesecond flow path comprises a space in the catalytic external to thetubular conduit.
 15. The fuel tank inerting system of claim 1, furthercomprising a second barrier between the second flow path and the thirdflow path, said second barrier being thermally conductive andimpermeable to fluids.
 16. The fuel tank inerting system of claim 1,further comprising a controller configured to control at least one of aflow rate of the first reactant, a flow rate of the second reactant, ora flow rate of the fluid coolant.
 17. The fuel tank inerting system ofclaim 16, wherein the controller is configured to control at least oneof the first reactant flow rate, the second reactant flow rate, or thefluid coolant flow rate to maintain a temperature in the catalyticreactor or at an outlet of the catalytic reactor.
 18. The fuel tankinerting system of claim 17, wherein the controller is configured tomaintain the temperature at less than 300° C.
 19. A method of operatingthe fuel tank inerting system of claim 1, comprising delivering thefirst and second reactants to the first and second inlets and deliveringthe fluid coolant to the third inlet, reacting the first and secondreactants along the reactive flow path to produce inert gas, anddelivering the inert gas through the inert gas flow path to the fueltank.
 20. The method of claim 19, further comprising controlling atleast one of a flow rate of the first reactant, a flow rate of thesecond reactant, or a flow rate of the fluid coolant to maintain atemperature in the catalytic reactor or at an outlet of the catalyticreactor.